1. Field of the Invention
The present invention relates to a device for feeding stock sheets one after another, and more particularly, to a device adapted to feed carton blanks as stock sheets to a packaging machine.
2. Description of the Related Art
Feeding devices of this type are described in Jpn. UM Appln. KOKOKU Publication No. 6-30644 and Jpn. Pat. Appln. KOKAI Publication No. 2-127226, individually, for example. These conventional feeding devices comprise a hopper for stock sheets. A large number of stock sheets are stored upright in the hopper. Suction pads are arranged for movement in the vicinity of an outlet of the hopper. The suction pads attract by suction a leading stock sheet having reached the hopper outlet, and draw it out from the hopper through the outlet.
The feeding devices further comprise a rotatable delivery roller, which is located at a predetermined distance from the hopper outlet, and the outer peripheral surface of which slightly projects from the bottom wall of the hopper. As the delivery roller rotates, it can deliver the stock sheets in the hopper to the hopper outlet. The rotation of the delivery roller and its suspension are controlled in accordance with the number of stock sheets stored in an outlet region between the roller and the hopper outlet.
More specifically, a sensor is located over the delivery roller, and the sensor is used to detect the degree of storage of the stock sheets in the starting end of the outlet region directly on the downstream side of the delivery roller. As the stock sheets are drawn out repeatedly through the hopper outlet, those sheets which are in the outlet region of the hopper are guided in succession to the hopper outlet. Accordingly, the number or storage degree of the stock sheets remaining in the starting end of the outlet region decreases gradually. The sensor detects the degree of storage of the stock sheets, and outputs a detection signal when the piling degree is reduced to a predetermined or lower value. In response to this detection signal output, the delivery roller is rotated to deliver new stock sheets into the output region of the hopper.
Since the stock sheets are delivered intermittently into the output region of the hopper, as described above, the degree of storage of the stock sheets in the outlet region varies, which makes the operation of the suction pads for drawing out the sheets unstable. If the degree of storage of the stock sheets in the outlet region is too low, the suction pads cannot adhere satisfactorily to the leading stock sheet, possibly failing to attract it by suction. If this storage degree is too high, on the other hand, the force of adhesion between the adjacent stock sheets is great. When the suction pads attract and draw out the leading stock sheet, therefore, a succeeding stock sheet may stick to the leading one in some cases. The frequency of this awkward phenomenon increases in proportion to the speed at which the stock sheets are drawn out from the hopper.